1. Field of the Invention
The present invention relates to a combined optical and electrical transmission assembly, which combines light and electricity to transmit signals and electrical power, and to a combined optical and electrical transmission module for electrical-to-optical or optical-to-electrical conversion.
2. Description of the Related Art
In recent years, with increasing display resolution and with increasing data dealt by information transmission device or storage device, there is an increasing demand for high-speed transmission lines capable of high-speed transmission of data. As high-speed transmission lines, there are used coaxial cables having a shield function, or differential transmission lines comprising a pair of differential lines in a shield, but their transmission distance is limited because of problems of noise or skew.
As a solution to this, there is a method that provides optical transmission lines between a computer and a monitor, or between servers, between which information signals are transferred, for optical transmission.
As devices used in these optical transmissions, there is a combined optical and electrical cable connected with a module at both its ends having an electrical connector for connecting, via an optical fiber, or a combined optical and electrical cable, optical devices such as LDs (laser diodes), PDs (photodiodes), or the like, a module comprising an IC (integrated circuit) for driving them, and an information transmission device or a storage device.
To drive the IC built in the module, JP-A-2000-214972 discloses use of electrical power supplied from the device, through the same connector as that connected with signal lines.
As prior art, there are JP-A-2000-214972 and JP-A-2002-366340.
When the module disposed to the combined optical and electrical cable is driven by using power supplied from an external device such as the information transmission device, storage device or the like, voltage of the power supplied is not always the same as voltage of driving the IC within the module. This restricts the IC that is possible to be used.
Also, typically, in high-speed IF (interface) without standardized optical transmission being taken into account, power is not assumed to be supplied to the IC driving the optical device, and power is separately required for driving the IC. To separately supply power for driving the IC, exclusive cables or connectors are separately required, which also complicates construction, causing problems with handling and cost.
Also, mounting the optical device typically requires a high mounting accuracy of not more than 10 μm, whereas mounting power cables permits a not less than 10-fold mounting error compared with mounting the optical device, and electrical signal line mounting accuracy is between optical device mounting accuracy and power cable mounting accuracy. Mounting those with different mounting accuracy on the same substrate requires matching to the strictest mounting accuracy specifications, which makes it difficult to fabricate the substrate, and makes the substrate costly.
Further, the high-speed electrical IF connector is not assumed to be used in optical connection, and its connection strength is weaker than that of a typical optical IF connector. This causes the problem that when the connector is pulled, the connector tends to slip out of a connector of the external device, which may cause an abrupt voltage change in the optical device, leading to a breakdown of the optical device.